Signing a PDF on a laptop, an iPhone or an Android phone

A contract lands while you are away from your desk

Daniel runs a two-person design studio. At 4:10 on a Thursday a client emails services_agreement_v3.pdf, four pages, with a note: sign page 4, initial pages 1 to 3, send it back before 6 so the project can start Monday. Daniel is on a train with an Android phone. His partner, at the office, has a Windows PC and an iPad. Who signs, and on what, decides which route is quickest.

The answer is rarely a special app. Each major platform either ships something that can place a signature or runs a browser that can. What differs is how much you can trust the result to look right on the other side, and how many taps it costs.

Which route suits which device

Mac, Windows and borrowed computers

Mac. Open the file in Preview and show the markup toolbar. Its signature control lets you write your name on the trackpad or hold a signature you wrote on paper up to the camera; the camera version usually looks far better. Preview keeps the signature for next time, so the second contract takes seconds.

Windows. The free Adobe Acrobat Reader has a fill-and-sign feature that stores a drawn or typed signature for reuse. Edge opens PDFs too and lets you draw on them, which works in a pinch, but a mouse scribble rarely looks like the signature on your passport.

Chromebook, Linux or someone else's PC. Skip the installs. Sign PDF runs in the tab, keeps the file on that machine and asks for no account. If the agreement came as a Word file rather than a PDF, the Word signing guide covers the conversion first.

iPhone and iPad: Markup does the job

Save the attachment to Files, open it there, and tap the Markup pen. The signature option sits with the text and shape tools; if the layout has changed in your iOS version, look for a plus button. A finger is fine, an Apple Pencil is better, and iOS remembers the signature for later documents.

Opening Markup straight from a Mail attachment saves a step, because the edited copy can go back as a reply. The one habit worth forcing: pinch-zoom on the signature line before you let go of the mark, since a signature placed at full-page zoom tends to land a few millimetres off.

Android: the browser is the safe bet

Android has no signing tool shared by every phone. Some makers bundle a notes or file viewer with a pen tool, others ship nothing that edits a PDF, so the honest advice is to check what your phone has and not count on it.

The browser behaves the same on every model. Open Sign PDF in Chrome, tap Choose a PDF, and pick the attachment from Downloads or from your mail app's saved files. Drawing with a fingertip on a phone screen gives a more natural stroke than a mouse ever does. If the PDF also has blanks to type into, finish those first with the steps in filling a form on your phone.

Sign PDF, the same five steps everywhere

1. Open Sign PDF and choose the file. It opens in the tab and is not uploaded.
2. Pick Draw, Type or Upload. Typed names use a cursive font; an uploaded PNG or JPG can have its light paper background removed.
3. Go to the right page, press Place signature, drag the mark onto the line and adjust it with the size control. Initials, the date and short text have their own buttons.
4. Press Add marks to PDF. The copy is reopened and checked: every mark must be visible, and the page geometry and selectable text must match the original.
5. Download the signed PDF under a new name, for example services_agreement_v3_signed.pdf, so the unsigned version stays intact.

The date button writes today's date in the format your browser uses. If the contract prints dates another way, type the date into the Text field instead. A walk-through of making a clean signature image lives in the handwritten signature guide.

Slips that get a signed file sent back

• Signed an older draft. Two versions sat in Downloads and the wrong one got the mark. Check the version number or date in the file before you open the tool, not after.
• Initials missing on one page. Phones make it easy to skip a page while swiping. Step through every page once more before you press the final button.
• Signature floating above the line. Zoom in, drag it down until the bottom of the strokes touches the line, and shrink it to roughly the height of the surrounding text.
• The file bounced for size. A photographed signature can add weight to a small file. Compress PDF can bring it under a mailbox limit.
• A warning about signature fields. Sign PDF shows it when the PDF has signature fields. If somebody has already applied a certificate signature, adding marks can invalidate it, so ask the sender before you confirm.

When a browser or a phone is the wrong tool

If the request says qualified, certified, or verifiable signature, or names a signing portal, a picture of your handwriting will not do, on any device. Use the service or certificate the sender names; the comparison of the two signature types explains how to read the request.

Company devices are another case. If your employer manages the laptop and restricts web tools, use the approved signing software or ask IT. And if the sender runs an e-signature platform, sign inside their link; downloading and returning a separate copy only confuses their audit trail.